SCIPP Seminar Archive


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Spring Quarter 2012 Archive

Last updated: June 8, 2012

Tuesday, June 5: 10:30am
Location: ISB 102
Marcos Lopez-Caniego (Instituto de Fisica de Cantabria)

Mining the Herschel-ATLAS: Submillimeter-selected Blazars in Equatorial Fields


The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an unprecedented opportunity to search for blazars at sub-mm wavelengths. We cross-matched the FIRST radio source catalogue with the 11655 sources brighter than 35 mJy at 500μm in the 135 square degrees of the sky covered by the H-ATLAS equatorial fields at 9 h and 15 h, plus half of the field at 12 h. We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10 arcsec, including 8 catalogued blazars (plus one known blazar that was found at the edge of one the H-ATLAS maps). To search for additional blazar candidates we have devised new diagnostic diagrams and found that known blazars occupy a region of the log(S500μm/S350μm) vs. log(S500μm/S1.4GHz) plane separated from that of the other sub-mm sources with radio counterparts. Using this diagnostic we have selected 12 further candidates that turn out to be scattered in the (r-z) vs. (u-r) plane or in the WISE color-color diagram proposed by Massaro et al. (2012), where known blazars are concentrated in well defined strips. This suggests that the majority of them either are not blazars or have spectral energy distributions contaminated by their host galaxies. A significant fraction of true blazars are found to be hosted by star-forming galaxies. This finding, supported by an analysis of blazars detected in Planck 545 and 857 GHz bands, is at odds with the notion that blazar hosts are passive ellipticals and indicates that the sub-mm selection is providing a novel prospect on blazar properties. Based on an inspection of the available photometric data, including the WISE all-sky survey, the unpublished VIKING survey and new radio observations, we tentatively estimate that there are 11 blazars with synchrotron flux density S500μm > 35mJy over the considered area. This result already allows us to constrain blazar evolution models.

Tuesday, May 29: 10:30am
Location: ISB 102
Keith Bechtol (Stanford)
Title: Unbeamed extragalactic emitters and the origin of the gamma-ray background


The extragalactic background light (EBL) represents the total emission from the edge of our Galaxy to the edge of observable Universe. In the gamma-ray band, the EBL becomes a census of high-energy activity over cosmic time. However, interpretation of the gamma-ray sky has proven challenging because only a limited number of bright extragalactic sources have been individually resolved from the background haze. Individually identified sources consist almost exclusively of active galactic nuclei (AGN) whose emission is enhanced by relativistic beaming, but observations with the Fermi Gamma-ray Space Telescope (Fermi) have started to reveal new types of extragalactic sources. I will provide a historical context of EBL studies in the gamma-ray band, and describe how Fermi is helping us to better understand populations of faint extragalactic sources such as non-AGN star-forming galaxies, AGN lacking powerful relativistic jets, and galaxy clusters.

Tuesday, May 22: 10:30am
Location: ISB 102
Tim Linden (UCSC)
Title: Understanding High Energy Emission from the Galactic Center: 2.5 Convincing Stories


Recent data taken at TeV energies (by Atmospheric Cherenkov Telescopes) and at GeV energies (by the Fermi-LAT) have opened a new window into studies of the Galactic center. These high-energy observations are especially well-suited to understanding the many energetic processes occurring in this region, and studies over the past several years have already discovered several new phenomena such as the Fermi bubbles and an apparent excess with a typical energy of approximately 1 GeV which is strongly peaked around the galactic center. In this talk, we will discuss several convincing models for the emission from this region, including the annihilation of particle dark matter, a yet-undiscovered population of millisecond pulsars, and finally proton emission from the central black hole. Finally, we will look at the potential for future experiments, such as the Cherenkov Telescope Array (CTA) to distinguish between these models.

Thursday, May 17: 2:00pm
Location: ISB 126
Sander Mooij (NIKHEF, Amsterdam, Netherlands)
Title: Sgoldstino Inflation


We discuss the possibility that inflation is driven by the sgoldstino, the superpartner of the goldstino. Unlike in generic supergravity scenarios, the sgoldstino decouples from all other fields in the theory, which allows for a simple and robust inflationary model. We argue that the two-field model given by this single complex scalar correctly captures the full multifield inflationary phenomenology. On the other hand, the assumption of stability, along the entire inflationary trajectory, of the supersymmetry--preserving sector that is integrated out leads to supplementary constraints on the parent supergravity. We investigate small field, large field and hybrid sgoldstino inflation scenarios and provide some working examples. They are subject to the usual fine-tuning issues that are common to all supergravity models of inflation.

Tuesday, May 15: 10:30am
Location: ISB 102
Douglas Bryman (University of British Columbia)
Title: Kaons Redux: Seeking New Physics with Rare Kaon Decays


Studies of rare decays of kaons have been important in establishing the current picture of particle physics and in constraining hypothetical new approaches which go beyond the Standard Model to deal with its known deficiencies. Experimental capabilities have increased in concert with theoretical understanding making this approach to searching for new physics more viable than ever and essential, even in the era of the LHC. In this talk, I will discuss the most interesting and incisive rare kaon decays, the "golden" ultra-rare reactions . In particular, the newly proposed ORKA experiment at Fermilab aimed at 1000 event sensitivity for offers the prospect of a major advance in the near term. Future opportunities at high intensity proton accelerators will also be discussed.

Please note special time and location:
Tuesday, May 8: 2:00pm
Location: ISB 235
Mariangela Lisanti (Princeton Center for Theoretical Science)
Title: A Flow of Dark Matter Debris: Exploring New Possibilities for Substructure


Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended ``debris flows'' in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.

Tuesday, May 1: 10:30am
Location: ISB 102
Henry Band (Univ. of Wisconsin-Madison)
Title: Observation of electron-antineutrino disappearance at Daya Baypdf:Henry_Band


The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle θ13 with a significance of 5.2 standard deviations in 55 days of data. Six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls will continue to accumulate data until summer 2012 when the final two antineutrino detectors will be installed. The status of the present analysis and future plans will be presented.

Tuesday, April 24: 3:00PM
Location: ISB 102
Leonardo Senatore (Stanford)
Title: On Loops and IR effects in Single Clock Inflation


Studying loop corrections to inflationary perturbations, with particular emphasis on infrared factors, is important to understand the consistency of the inflationary theory, its predictivity and to establish the existence of the slow-roll eternal inflation phenomena and its recently found volume bound. I will discuss how large IR effects appear in these calculations, how some of them disappear when we compute fluctuations as a function of physically measurable scales, and finally how some of them remain and lead to interesting projection effects.

Tuesday, April 17: 10:30am
Location: ISB 102
John Rice (UC Berkeley)
Title: Hierarchical Search Method for Astrophysical Source Detection


Some astronomy projects require a blind search through a vast number of hypotheses to detect objects of interest. The number of hypotheses to test can be in the billions. A naive blind search over every single hypothesis would be far too costly computationally. We propose a hierarchical scheme for blind search, using various "resolution" levels. At lower resolution levels, "regions" of interest in the search space are singled out with a low computational cost. These regions are refined at intermediate resolution levels and only the most promising candidates are finally tested at the original fine resolution. The optimal search strategy is found by dynamic programming. We demonstrate the procedure for pulsar search from satellite gamma-ray observations and show that the power of the naive blind search can almost be matched with the hierarchical scheme while reducing the computational burden by more than three orders of magnitude.

Tuesday, April 10: 10:30am
Location: ISB 102
Tim Tait (UC Irvine)
Title: Fun with Effective Theory Descriptions of Dark Matter


I'll explore effective quantum field theory descriptions of dark matter, and show how they allow for an interesting language to talk about the properties of WIMPs. Because they capture the most important features of many specific models, they also allow a more straight-forward comparison of searches for dark matter directly, indirectly, and at colliders.

Tuesday, April 3: 10:30am
Location: ISB 102
Troy Porter (Stanford)
Title: Cosmic Rays in the Milky Way and Other Galaxies


Cosmic rays fill up the entire volume of galaxies, providing an important source of heating and ionisation of the interstellar medium, and may play a significant role in the regulation of star formation and evolution of galaxies. Diffuse emissions from radio to high-energy gamma rays (> 100 MeV) arising from various interactions between cosmic rays and the interstellar medium, interstellar radiation field, and magnetic field, are currently the best way to trace the intensities and spectra of cosmic rays in the Milky Way and other galaxies. I will talk about our recent work investigating the cosmic-ray induced emissions from our own and other galaxies using multi-frequency data and the GALPROP cosmic ray code.